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Here, a unique heteroatom-doped spongy carbonaceous material from dwarf banana peel has been synthesized successfully using the one-step hydrothermal method. The discarded banana peel was reused as a carbon source for the formation of heteroatom-doped porous carbon. This biowaste-derived heteroatom-doped porous carbonaceous material (BH-PCM) has plenty of interconnected pores with an acceptable surface area of 213 m2 g−1. Thoroughly characterized BH-PCM has been used as electrode material for supercapacitor using a three-electrode system with an aqueous 1 M H2SO4 solution. The as-synthesized BH-PCM holds an excellent specific capacitance of 137 F g−1 at 0.5 A g−1 and an impressive rate performance with a capacitance enduring 51 F g−1 at 5.0 A g−1. After 10,000 galvanostatic charge–discharge cycles, an initial capacitance of 94% was maintained. To show the practical applicability of the BH-PCM, the symmetrical two-electrode cell was fabricated and delivered the gravimetric specific capacitances of 87 F g−1 at 1 A g−1. The excellent electrochemical performance of BH-PCM towards supercapacitor was due to their high surface area, reasonable heteroatom doping rate, and a suitable degree of graphitization. This study offers a green approach for the development of environmental-friendly potential carbon-based electrode, by converting biowaste to clean/green energy.

The electrolysis of water is considered as a potentially realistic technology for the massive production of hydrogen. The use of graphene composites in electrocatalytic water splitting has been extensively investigated. Graphene-iron oxide composites were prepared via in situ polymerization of 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) and poly (ethylene glycol) monomethacrylate (PEG) on graphene surface (non-oxidative graphite-HOPG/G) in presence of iron oxide nanoparticles (IONPs) and denoted as G-INSCP. Copolymers PMPC-co-PEG (CP) and block copolymer PMPC-b-PEG (BCP) were prepared and their structures were thoroughly characterized. These polymers were used to prepare G-INSCP, G-CP, and G-BCP, their stabilities were compared and their morphologies were studied. HOPG, G-CP, and G-INSCP were used in the hydrogen evolution reaction (HER) as effective platinum catalyst alternatives. G-BCP composite was excluded owing to its very low stability. To evaluate the performance of these electrocatalysts in acidic media, linear sweep voltammetry and electrochemical impedance spectroscopy were employed. Results revealed that, compared with HOPG and G-CP, G-INSCP exhibited a significantly improved catalytic activity with respect to HER in an acidic electrolyte. Additionally, at a current density of 10 mA cm−2, G-INSCP demonstrated a lower overpotential and Tafel slope of 95 mVRHE and 67 mV dec−1, respectively. These observations were attributed to the synergistic effect between the magnetic IONPs and PMPC polymer along with the increase in the electron transfer rate owing to the conductive graphene in the catalyst. Thus G-INSCP catalyst can be a potential candidate for HER and paving the way for the advancement of new and similar catalysts for other applications.

Dumping of solid waste and draining of energy resources have become an escalating global issue by affecting the world’s ecology and economy through environmental pollution and fuel crisis. The prim...

Graphene is an excellent 2D material that has extraordinary properties such as high surface area, electron mobility, conductivity, and high light transmission. Polymer composites are used in many applications in place of polymers. In recent years, the development of stable graphene dispersions with high graphene concentrations has attracted great attention due to their applications in energy, bio-fields, and so forth. Thus, this review essentially discusses the preparation of stable graphene–polymer composites/dispersions. Discussion on existing methods of preparing graphene is included with their merits and demerits. Among existing methods, mechanical exfoliation is widely used for the preparation of stable graphene dispersion, the theoretical background of this method is discussed briefly. Solvents, surfactants, and polymers that are used for dispersing graphene and the factors to be considered while preparing stable graphene dispersions are discussed in detail. Further, the direct applications of stable graphene dispersions are discussed briefly. Finally, a summary and prospects for the development of stable graphene dispersions are proposed.

This article describes a simple preparation of chitosan/gelatin (CG) spherical hydrogel particles for the effective removal of multiple heavy metal ions. The CG hydrogel particles were prepared by inverse emulsion from the aqueous solutions of chitosan, gelatin, and glutaraldehyde. The oven-dried C2G1 hydrogel particles showed a maximum removal efficiency of 98% for Hg(II) ions in a single metal ion solution and which was higher than C1G1 (85%) and C1G2 (58%) particles. This result was affected by the composition of the hydrogels rather than the pore size or degree of swelling. Remarkably, the removal efficiencies for the Pb(II), Cd(II), Hg(II), and Cr(III) ions reached about 73%–94% in a multiple metal ion solution. The results indicate that the CG hydrogel particles can be used to remove coexisting heavy metal ions from wastewater, providing a versatile method to remove multiple metal ions from natural or industrial wastes.

In this work, nitrogen-doped carbon quantum dots (N-CQDs) have been synthesized successfully by a simple hydrothermal method and demonstrated its application for multicolor imaging in Caenorhabditis elegans (C. elegans) as an in vivo model. The synthesized N-CQDs were characterized by various physicochemical techniques such as XRD, Raman spectroscopy, ATR-FTIR spectroscopy, XPS, HRTEM, UV–vis spectroscopy, and fluorescence spectroscopy. The synthesized N-CQDs exhibited a strong fluorescence due to the uniform size distribution with nitrogen-containing and oxygen-containing functional groups onto the surface of N-CQDs which induce the excellent dispersibility in aqueous media. The N-CQDs has an excitation-dependent fluorescence behavior and the strongest fluorescence appeared at 411 nm (emission peak position) under the excitation of 340 nm. Also, the N-CQDs displayed a high quantum yield (QY) of 12.5. The fluorescence behaviour of the aqueous N-CQDs suspension retains for a long time up to 1 year. The prolonging fluorescent N-CQDs was utilized as a staining agent for bioimaging and toxicity of N-CQDs on C. elegans that was conducted by killing assay. In-vivo studies suggested that the N-CQDs displayed excellent biocompatibility and successfully used for high-contrast imaging of N-CQDs in living and dead C. elegans. Based on the strongest fluorescence along with excellent aqueous dispersibility and biocompatibility, the green synthesized N-CQDs would be an ideal candidate for many biological applications.

The iron-oxide nanoparticles (IONPs) filled multi-walled carbon nanotubes (IONP-MWCNTs hybrid) were directly synthesized via chemical vapour deposition method with acetylene as a carbon source. The bare IONPs were synthesized by hydrothermal method and the prepared bare IONPs were employed as a catalytic-support as well as a filling agent for the synthesis of IONP-MWCNTs hybrid at about 800 °C under atmospheric pressure. The synthesized IONP-MWCNTs hybrid was characterized by various physicochemical techniques including X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy and high-resolution transmission electron microscopy. The results demonstrate that the carbon nanotubes were successfully generated on the IONPs with the high yield because of unique carbon-iron metal interactions. An average diameter of synthesized IONPs and MWCNTs are around 9 and 50 nm, respectively. In addition, the HRTEM images and Raman spectrum confirms the obtained IONP-MWCNTs hybrid is well graphitic without major carbonaceous impurities. The electrochemical activity of the synthesized IONP-MWCNTs hybrid was performed in 2 M KOH using a three-electrode cell setup with a saturated Ag/AgCl as a reference electrode and a platinum plate as a counter-electrode by cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy techniques. This electrode active material (IONP-MWCNTs hybrid) possess excellent supercapacitive behaviour and has excellent cyclic stability, even after 5000 cycles of charge-discharge at 4 A g−1 as current density. Thus, the synthesized IONP-MWCNTs hybrid will be a suitable as well as an economical electrode active material for high-performance supercapacitors.

Sulphur and nitrogen-rich carbon layers (S/N-CLs) have been derived successfully via a simple calcination for high energy applications including supercapacitor and electrocatalytic hydrogen evolution reaction (HER). The flexible working electrode was fabricated using thoroughly analyzed S/N-CLs composite as an active electrode energy material for supercapacitor and HER. The S/N-CLs composite shows a higher specific capacitance of 266 F g−1 at a current density of 0.5 A g−1 and a satisfied cycling stability with 84% capacitance retention even after 5000 cycles of galvanostatic charge-discharge. On the other hand, the synthesized S/N-CLs composite was used as an electrocatalyst for HER and it exhibits an excellent HER performance with an onset overpotential of −75 mV, and a Tafel slope of 73 mV dec−1 in 0.5 M H2SO4 aqueous electrolyte. Also, the S/N-CLs composite displayed good stability and strong durability. The high electrocatalytic activity and stability of S/N-CLs composite toward HER due to the active site of a compound which may originate from the heteroatom-functional groups including N and S in the carbon structure. Overall, the high-performance supercapacitors and enhancing HER based on heteroatom-doped carbon structures could be promising in replacing traditional supercapacitors for many electronic devices and electrocatalyst for HER.

We report the synthesis of eco-friendly fluorescent nitrogen-doped carbon dots (NCDs) using the renewable resource of Phyllanthus emblica juice as a precursor by the hydrothermal process at 200 °C ...

As an efficient photocatalytic titanium dioxide nanoparticles@nitrogen-doped carbon (TiO2 NPs@C) nanocomposite and bright fluorescent with good biocompatible nitrogen-doped carbon dots (N-CDs) were synthesized at once by an affordable hydrothermal method. Physicochemical properties of the synthesized materials were examined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) with energy dispersive X-ray (EDX) and elemental mapping analysis, high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), ultraviolet–visible (UV–vis) spectroscopy and fluorescence spectroscopy. The photocatalytic efficiency of synthesized TiO2 NPs@C nanocomposite was evaluated in the degradation of methylene blue (MB) under UV-light irradiation. The degradation efficiency of TiO2 NPs@C nanocomposite is about 90% when extending the irradiation time to 40 min, the rate constant is 5 times higher than that of bare TiO2 NPs. The augmentation of photocatalytic activity of TiO2 NPs@C nanocomposite was attributed to the synergistic effect between TiO2 NPs and graphene-like carbon within the nanocomposite. The recycling studies were conducted and the photodegradation efficiency of TiO2 NPs@C nanocomposite did not show any significant changes up to three cycles, suggesting that the synthesized photocatalyst has good repeatability and the considerable stability. In addition, the carbon derived from a natural green source possesses the hydroxyl and nitrogen-containing functional groups on the surface which resulting TiO2 NPs @C nanocomposite with high photocatalytic activity. Also, the obtained N-CDs displays almost zero toxicity towards the Candida albicans cells even at high concentrations which can be utilized as a powerful in-vitro label-free fluorescent probe for live cell imaging. Based on their bright with stable fluorescence and cellular imaging with good biocompatibility, N-CDs would offer a great potential for a wide range of applications in the biomedical and clinical applications in the near future.

Hexagon-shaped composite made up of iron oxide nanoparticles@carbon (IONP@C-HIOP) was successfully synthesized at 185 °C by a simple hydrothermal method. All the analytical results confirmed the formation of IONP@C-HIOP with a uniform size without apparent aggregation. The IONP@C-HIOP composite exhibits excellent catalytic activity towards hydrogen evolution reaction (HER) with lowest onset-potential (−25 mVRHE) and Tafel slope (45 mV dec−1) in 0.5 M H2SO4 aqueous electrolyte. The high electrocatalytic performance of the composite towards HER attributes to the carbon decorated IONPs, providing a conducting network for fast electron transport from IONPs to electrodes. The composite shows high stability representing a synergistic effect between IONPs and carbon for efficient HER. In addition, the supernatant solution (byproduct) of IONP@C-HIOP showed durable fluorescence activity and was used as a label-free fluorescent probe for live cell imaging applications. This method of synthesis is a simple and economic for multi-diverse applications. Thus, the main product of synthesized IONP@C-HIOP might be an ideal choice for environmental-friendly applications HER and the byproduct for cell imaging.

The present work illustrates the potential uses of nitrogen-doped multi-fluorescent carbon dots (N-CDs) for Fe3+ sensing, cellular multi-colour imaging, and fluorescent ink. N-CDs were synthesized using Magnolia liliiflora flower by the simple hydrothermal method. The resulted N-CDs was found to be nearly spherical in shape with the size of about 4 ± 1 nm and showed competitive quantum yield around 11%. The synthesized N-CDs with uniform size distribution and high content of nitrogen and oxygen-bearing functional groups exhibit excellent dispersibility in aqueous media. The N-CDs were able to detect a high concentration of Fe3+ ions (1–1000 μM) with a limit of detection is about 1.2 μM by forming N-CDs-Fe3+ complex due to the functional groups such as nitrogen, carbonyl and carboxyl on the surface of N-CDs. Thus they could be used to remove pollutants from industrial wastewater. The electronic charge on the surface of the N-CDs and N-CDs-Fe3+ complex (zeta potential) is around −36 and 18 mV, respectively. In addition, these N-CDs show excitation-dependent fluorescence that was utilized for multi-colour in vitro cellular imaging in rat liver cells (Clone 9 hepatocytes). The N-CDs are rapidly uptake in the cell cytoplasm and showed high cytocompatibility on cellular morphology. Moreover, as the N-CDs possess strong fluorescence and anti-coagulation they could be utilized in fluorescent ink pens.

Measurement of the interaction force between two materials provides important information on various properties, such as adsorption, binding, or compatibility for coatings, adhesion, and composites. The interaction forces of zwitterionic and ionic monomers with graphite platelets (G) and reduced graphene oxide (rGO) surfaces were systematically investigated by atomic force microscopy (AFM) in air and water. The monomers examined were 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate (MPC), [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBE), [2-(acryloyloxy)ethyl]trimethylammonium chloride (ATC), and 2-methyl-2-propene-1-sulfonic acid sodium (MSS). The AFM studies revealed that MSS and SBE monomers with sulfonate units have stronger interaction forces with G surface in air and that MPC and ATC monomers with quaternary ammonium units have higher interaction forces in water. In the case of rGO surface, the monomers with quaternary ammonium units showed stronger interactions regardless of the medium. These interactions could be rationalized by the interaction mechanism between the monomers with graphene surfaces, such as cation-π for MPC and ATC and anion-π for MSS and SBE. Overall, cation-π interactions were effective in water, whereas anion-π interactions are effective in air with G surface. The adhesion values of MPC, SBE, ATC, and MSS on rGO were lower than the values measured on G surface. Among the monomers, MPC showed the highest dispersibility for aqueous graphene dispersions. Further, the adsorption of MPC on G and rGO surfaces was verified by high-resolution transmission electron microscopy and X-ray diffraction patterns.

A new, highly selective, sensitive and stable enzymatic glucose sensor was fabricated on glassy carbon electrode (GCE) using zinc oxide (ZnO) nanoparticles embedded nitrogen-doped carbon sheets (ZnO@NDCS), glucose oxidase (GOx) (assigned as GCE/ZnO@NDCS/GOx). First, ZnO@NDCS were synthesized by a simple hydrothermal method. Zn powder, aqueous ammonia, and peach extract were served as the precursor for ZnO NPs, nitrogen and carbon, respectively. The fabricated GCE/ZnO@NDCS/GOx biosensor exhibited a high and reproducible sensitivity of 231.7 μA mM−1 cm−2. Also, showed a wide linear range from 0.2 to 12 mM with a correlation coefficient R2 = 0.998 and lowest detection limit (based on S/N ratio = 3) of 6.3 μM. The GCE/ZnO@NDCS/GOx biosensor is acceptably stable, selective, and it was successfully applied to the quantitative monitoring of glucose in human blood serum. The synthesized ZnO@NDCS nanocomposite may be found useful in other applications in the fields of solar cells and optoelectronic devices. These encouraging results suggest a simple and effective method obtain electrode material for the enzymatic glucose sensor.

Cobalt oxide nanoparticles@nitrogen-doped reduced graphene oxide (Co3O4@N-rGO) composite and nitrogen-doped graphene dots (N-GDs) were synthesized by a one-pot simple hydrothermal method. The average sizes of the synthesized bare cobalt oxide nanoparticles (Co3O4 NPs) and Co3O4 NPs in the Co3O4@N-rGO composite were around 22 and 24 nm, respectively with an interlayer distance of 0.21 nm, as calculated using the XRD patterns. The Co3O4@N-rGO electrode exhibits superior capacitive performance with a high capability of about 450 F g−1 at a current density of 1 A g−1 and has excellent cyclic stability, even after 1000 cycles of GCD at a current density of 4 A g−1. The obtained N-GDs exhibited high sensitivity and selectivity towards Fe2+ and Fe3+, the limit of detection was as low as 1.1 and 1.0 μM, respectively, representing high sensitivity to Fe2+ and Fe3+. Besides, the N-GDs was applied for bio-imaging. We found that N-GDs were suitable candidates for differential staining applications in yeast cells with good cell permeability and localization with negligible cytotoxicity. Hence, N-GDs may find dual utility as probes for the detection of cellular pools of metal ions (Fe3+/Fe2+) and also for early detection of opportunistic yeast infections in biological samples.

The hybrid composite of ZnO nanoparticles decorated nitrogen-doped graphitic carbon sheets (ZnO@N-C) alongside nitrogen-doped carbon dots (N-CDs) were synthesized by the direct hydrothermal method of peach fruit juice and ZnO nanoparticles (ZnO NPs). The synthesized ZnO@N-C hybrid composite and N-CDs were thoroughly characterized by various physicochemical techniques including powder X-ray diffraction (PXRD), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) with energy-dispersive X-ray (EDX) spectroscopy, high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, and fluorescence spectroscopy. The ZnO NPs were dispersed in the graphitic carbon structure with an average size of 25 ± 5 nm. The chemical composition of C, O, N, and Zn within the ZnO@N-C hybrid composite exhibits enough graphitization. Methylene blue (MB)-degradation was estimated utilizing the ZnO@N-C hybrid composite, a maximum degradation efficiency of >95% was achieved in a neutral aqueous medium within 60 min under UV-light irradiation. This maximum efficiency allows estimating the contribution of the heterogeneous and homogeneity of ZnO@N-C hybrid composite which is responsible for the MB-degradation. Moreover, the economic natural biosource or bio-waste was employed for the synthesis of ZnO@N-C hybrid composite and displays an excellent photocatalytic degradation under UV-light irradiation which is an alternate for other carbon-based metal oxides. In addition, the resulting N-CDs were utilized as a fluorescence probe for cellular imaging, owing to their tremendous properties such as bright fluorescence with high quantum yield, excellent water solubility, and good biocompatibility. The N-CDs displays a multicolour fluorescence based on their changing of excitation wavelength and these multicolour fluorescence emissions offered a multicolour cellular imaging which could be applicable for real biological system in the near future.

A facile, economical and one-step hydrothermal method is used to synthesize highly durable fluorescent nitrogen-doped carbon dots (FNCDs) by utilizing Phyllanthus acidus (P. acidus) and aqueous ammonia as the carbon and nitrogen sources, respectively. The synthesized FNCDs have an average size of 4.5±1nm and showed bright blue fluorescence under the irradiation of UV-light at an excitation wavelength of 365nm. It exhibits a quantum yield (QY) of 14% at an excitation wavelength of 350nm with maximum emission at 420nm. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy characterizations clearly showed the formation of FNCDs that predominantly consists of nitrogen and hydroxyl groups which can provide more adsorption sites. In addition, the above study reveals the successful bonding of nitrogen with carbon (C-N) in the FNCDs. The synthesized FNCDs with high QY can be used as efficient fluorescent probes for the detection of Fe3+. Based on the linear relationship between normalized fluorescence intensity and concentration of Fe3+ ions, the prepared FNCDs can be used for label-free sensitive and selective detection of Fe3+ ions in a wide concentration range of 2-25μM with a detection limit of 0.9μM. The present study proves that synthesized FNCDs has durable fluorescence, soluble in water very well and thus act as a promising candidate for the diverse applications such as label-free sensitive and selective detection of Fe3+, fluorescent ink and cellular imaging with good biocompatibility and low cytotoxicity.

Deep eutectic solvents (DES) are considered as a green non-toxic electrolyte for the replacement of cyanide based toxic electrolytes towards the electrodeposition of noble metal and alloy nanoparticles on conducting surfaces. In this work, ruthenium nanoparticles (RuNPs) are electrochemically synthesized over cathodically treated stainless-steel mesh (CSS) by applying the cathodic current of −15 mA/cm2 using ruthenium chloride and deep eutectic mixture consists of choline chloride/urea as electrolyte. The resulting material is abbreviated as RuNPs@CSS and are characterized by surface analytical tools such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning elctron microscopy with energy dispersive spectrum (FE-SEM with EDS). Further, the electrocatalytic hydrogen evolution reaction (HER) activity of RuNPs@CSS is accessed and compared with state of art Pt electrode using open circuit potential (OCP), linear sweep voltammetry (LSV), Tafel plot and electrochemical impedance spectroscopy (EIS) measurements in 0.5 M H2SO4. The calculated HER's onset potential and over potential @ −10 mA/cm2 of RuNPs@CSS are about −0.0273 and −0.0657 V vs. RHE, which are very close to the bare Pt values. The EIS results suggested that, RuNPs@CSS possess excellent conductivity, which decrease the charge transfer resistance and enhances the HER. This study proved that the electrodeposited RuNPs@SS is better replacement for Pt based electrocatalysts towards acidic HER.

Recently, carbon dots (CDs) have received increasing attention, and several reports have indicated that CDs are promising fluorescent carbon-based materials. CDs present outstanding physical and chemical properties because of their excellent properties, CDs are used in a wide range of applications, such as bioimaging, sensing, drug delivery, and nanoelectronics. Numerous approaches can be used to prepare CDs, such as arc discharge, laser ablation, electrochemical exfoliation, chemical oxidation, ultrasonic passivation, combustion, microwave pyrolysis, the template method, and the hydrothermal method. In addition, basic techniques used for the separation of CDs are included and discussed shortly. In this short review, the synthesis and characterization of CDs from plant sources using the eco-friendly hydrothermal method is described. Further, the importance of hydrothermally synthesized CDs is discussed briefly. The applications and advantages of CDs in bioimaging, fluorescent inks, and detections or sensing are also reported herein. Finally, we summarize the importance, challenges, and future direction towards the research of CDs.

Recently, the use of natural products for the synthesis of carbon dots (CDs) has received much attention. Herein, leftover kiwi (Actinidia Deliciosa) fruit peels were successfully turned into beneficial fluorescent carbon dots (KN-CDs) via the hydrothermal-carbonization route. KN-CDs 1 and KN-CDs 2 were prepared without and with ammonium hydroxide, respectively. KN-CDs 1 and KN-CDs 2 were systematically characterized by various analytical techniques. Synthesized KN-CDs showed spherical-shaped morphology with narrow size distribution and excellent optical properties with excitation-independent behaviors. The quantum yields of KN-CDs 1 and KN-CDs 2 were calculated as 14 and 19%, respectively. Additionally, the KN-CDs possess excellent prolonging and photostability. Because of the excellent optical properties of KN-CDs, they were utilized as fluorescent sensors. The strong fluorescence of the KN-CDs was selectively quenched by Fe3+ ion, and quenching behavior showed a linear correlation with the concentrations of Fe3+ ion. KN-CDs 1 and KN-CDs 2 showed the detection of Fe3+ ions within the concentration range of 5–25 µM with the detection limit of 0.95 and 0.85 µM, respectively. Based on the turn-off sensing by the detection of Fe3+ ions, KN-CDs would be a promising candidate as a selective and sensitive fluorescent sensor.

Anchoring electrocatalyst nanoparticles on carbon materials is a promising strategy to establish a hybrid electrocatalyst with unique structure and properties. Deriving carbon support from waste materials is an environmentally green approach. In the present study, the pyrolysis of the heterogeneous mixture containing synthetic disposal material and nickel salt yields N-doped carbon fibers-supported nickel oxide (NiO@CFs) hybrid electrocatalyst. The NiO nanoparticles are well incorporated on the porous carbon base, which has densely packed sharp-edge carbon fibers (CFs). The unique carbon structure incorporated with the NiO nanoparticles that facilitates the adsorption of electrolyte ions, rushes the transfer of electrolyte ions, and thus enhances the electrochemical activity. The as-derived carbon support maximized the electrocatalyst active sites while utilizing low electrocatalyst mass loading. Specifically, the synthetic disposable material-derived-carbon fibers supported NiO (NiO@CFs) hybrid electrocatalyst exhibited remarkably higher surface area and lower charge transfer resistance when compared to that of bare NiO. Intriguingly, the NiO@CFs hybrid electrocatalyst exhibited desirable oxygen evolution reaction (OER) performance (η = 280 mV at 10 mA cm−2) and consistent durability for a 24 h continuous run. This study emphasizes that the utilization of synthetic disposal materials for deriving carbon support is an environmentally effective methodology to incorporate/hybridize electrochemically active materials for the various electrochemical applications.

In this work, we have demonstrated a prompt anodic electrochemical exfoliation of graphite into graphene sheets (GS) in aqueous media. For the synthesis of GS, a constant potential of +10 V has been applied between two identical graphite sheets in 0.1 M aqueous ammonium sulfate. The exfoliated GS were characterized via standard analytical tools such as Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy with energy dispersive spectrum (FE-SEM with EDS). Further, the electrochemical performance of GS coated Ni foam (GS/Ni foam) was assessed by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) techniques in 2 M KOH. The quasi-rectangular shaped voltammograms and triangular shaped GCD curves in a three-electrode system was evidenced the double-layer capacitance of GS/Ni foam, which exhibited maximum specific capacitance of 84.82 and 40. 83 F/g at 2 mV/s, and 0.1 A/g of current density, respectively. Moreover, the symmetric two-electrode performance of GS/Ni foam was also examined, which showed good energy density (3.03 Wh/kg) and power density (562.5 W/kg). This study proves that the anodically exfoliated GS can act as a good symmetric supercapacitor in KOH.

The growth of industry fulfills our necessity and promotes economic development. However, pollutants from such industries pollute water bodies which pose a high risk for living organisms. Thus, researchers have been urged to develop an efficient method to remove toxic heavy metal ions from water bodies. The adsorption method shows promising results for the removal of heavy metal ions and is easy to operate on a large scale, thus can be applied to practical applications. Numerous adsorbents were developed and reported, among them hydrogels, which attract great attention because of the reusability, ease of preparation, and handling. Hydrogels are generally prepared by the cross-linking of polymers that result in a three-dimensional structure, showing high porosity and high functionality. They are hydrophilic in nature because of the functional groups, and are non-toxic. Thus, this review provides various methods of hydrogel adsorbents preparation and summarizes recent progress in the use of hydrogel adsorbents for the removal of heavy metal ions. Further, the mechanism involved in the removal of heavy metal ions is briefly discussed. The most recent studies about the adsorption method for the treatment of heavy metal ions contaminated water are presented.

Nitrogen-doped carbon dots (N-CDs) were synthesized from Chionanthus retusus (C. retusus) fruit extract using a simple hydrothermal-carbonization method. Their ability to sense metal ions, and their biological activity in terms of cell viability and bioimaging applications were evaluated. The resulting N-CDs were characterized by various physicochemical techniques such as high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Raman spectroscopy. The optical properties were characterized by ultraviolet visible (UV-vis) fluorescence spectroscopy techniques. The average size of the N-CDs was approximately 5 ± 2 nm with an interlayer distance of 0.21 nm, as calculated from the HRTEM images. The presence of phytoconstituent functionalities and the percentages of components in the N–CDs were confirmed by XPS studies, and a nitrogen content of 5.3% was detected. The N–CDs demonstrated highly durable fluorescence properties and low cytotoxicity with a quantum yield of 9%. The synthesized N–CDs were then used as probes for the detection of metal ions. The N–CDs exhibited high sensitivity and selectivity towards Fe3+, with a linear relationship between 0 and 2 μM and a detection limit of 70 μM. The synthesized N–CDs are anticipated to have diverse biomedical applications, particularly for bioimaging, given their high fluorescence, excellent water solubility, good cell permeability, and negligible cytotoxicity. Finally, the potential of N–CDs as biological probes was investigated using fungal (Candida albicans and Cryptococcus neoformans) strains via fluorescent microscopy. We found that N–CDs were suitable candidates for differential staining applications in yeast cells with good cell permeability, localization with negligible cytotoxicity. Hence, N–CDs may find dual utility as probes for the detection of cellular pools of metal ions (Fe3+) and also for early detection of opportunistic yeast infections in biological samples.

This article describes a comprehensive study for the preparation of graphene dispersions by liquid-phase exfoliation using amphiphilic diblock copolymers; poly(ethylene oxide)-block-poly(styrene) (PEO-b-PS), poly(ethylene oxide)-block-poly(4-vinylpyridine) (PEO-b-PVP), and poly(ethylene oxide)-block-poly(pyrenemethyl methacrylate) (PEO-b-PPy) with similar block lengths. Block copolymers were prepared from PEO using the Steglich coupling reaction followed by reversible addition-fragmentation chain transfer (RAFT) polymerization. Graphite platelets (G) and reduced graphene oxide (rGO) were used as graphene sources. The dispersion stability of graphene in ethanol was comparatively investigated by on-line turbidity, and the graphene concentration in the dispersions was determined gravimetrically. Our results revealed that the graphene dispersions with PEO-b-PVP were much more stable and included graphene with fewer defects than that with PEO-b-PS or PEO-b-PPy, as confirmed by turbidity and Raman analyses. Gravimetry confirmed that graphene concentrations up to 1.7 and 1.8mg/mL could be obtained from G and rGO dispersions, respectively, using PEO-b-PVP after one week. Distinctions in adhesion forces of PS, VP, PPy block units with graphene surface and the variation in solubility of the block copolymers in ethanol medium significantly affected the stability of the graphene dispersion.

Synthesis of an eco-friendly and efficient antibacterial and antifouling coatings is presented by exploiting urushiol, a natural varnishing material. Since urushiol has inherent outstanding surface-protecting and antimicrobial properties, a series of poly (methyl methacrylate)-urushiol polymer compositions were prepared and fabricated into films. The prepared films were subjected to antimicrobial and antifouling studies. The polymer systems were characterized by various physico-spectroscopic techniques such as 1H NMR, Fourier transform infrared spectroscopy, differential scanning calorimetry, atomic force microscopy, and thermal gravimetric analysis. The confocal laser scanning micrographs, obtained for Pseudomonas aeruginosa biofilm formation, demonstrated an excellent antimicrobial response of the urushiol-incorporated polymers against this bacterial strain. We also demonstrated an inhibitory attachment effect against Navicula incerta, a fouling microalgal strain.

Zinc oxide nanoparticles decorated graphene oxide (ZnO@GO) nanocomposite was successfully prepared using graphene oxide (GO) and zinc oxide nanoparticles (ZnO NPs) as raw materials by simple solvothermal method. The X-ray diffraction pattern, X-ray photoelectron spectroscopic, Fourier transform infrared spectroscopic, and Raman spectroscopic techniques revealed the formation, elemental composition and the purity of ZnO NPs and ZnO@GO nanocomposite. The ZnO NPs were synthesized via simple thermal oxidation, the synthesized ZnO NPs exhibits an excellent near spherical shape with narrow size distribution and mean size of around 20 ± 5 nm which is vividly observed from field emission scanning electron microscopic images. The elemental compositions of ZnO@GO nanocomposite which carbon, oxygen and zinc were revealed by XPS and EDX elemental mapping. The ZnO NPs decorated on GO layers were clearly seen in the high resolution transmission electron microscopic images. The photocatalytic activities of the synthesized pure ZnO NPs and ZnO@GO nanocomposite were investigated by photodegradation of azo-dyes includes neutral red (NR), crystal violet (CV), congo red (CR) and methyl orange (MO) under UV-light irradiation. The results revealed that the ZnO@GO nanocomposite exhibited a remarkably higher photocatalytic efficiency compared to pure ZnO NPs. The enhancement of photocatalytic performance was ascribed to the synergistic effect between ZnO NPs and GO layers. Hence, the synthesized ZnO@GO nanocomposite crucial for efficient degradation of dyes such as NR, CV, CR and MO. The synthesized ZnO@GO nanocomposite exhibits a good photocatalytic activity along with good reproducibility of photodegradation, which is applicable for practical applications.

Graphene oxide grafting titanium dioxide nanoparticles (TiO 2 -GO nanocomposite) was successfully synthesized by a simple solvothermal method. The synthesized TiO 2 -GO nanocomposite were systematically characterized by various physico-chemical techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The XRD results confirm the crystallinity of synthesized bare titanium dioxide nanoparticles (TiO 2 NPs), pristine graphene oxide (GO) and TiO 2 -GO nanocomposite with high pure in nature. The average size of the bare TiO 2 NPs was around 5 nm and were dispersed over the wrinkled graphene layers. Raman spectrum shows the resulting GO and TiO 2 -GO nanocomposite exhibit moderate graphitization with the intensity of D to G value was 1.1 and 1.2, respectively. The chemical state, functionality and composition (carbon, oxygen and titanium) of the resulting TiO 2 -GO nanocomposite were revealed by XPS analysis. The photocatalytic activity of synthesized TiO 2 -GO nanocomposite was investigated on the degradation of hazardous organic dyes (methylene blue (MB) and methyl orange (MO)) under UV-light irradiation and was compared with bare TiO 2 NPs and were presented based on the preferred propagation path of induced electrons that leads to generation of O 2 ─ . The resulting TiO 2 -GO nanocomposite achieve a maximum degradation efficiency of 100 and 84% on MB and MO in a neutral solution within 25 and 240 min, respectively under UV-light irradiation, the results show that the GO plays an important role in the enhancement of photocatalytic performance. The high photocatalytic efficiency due to the increased light absorption, the reduced charge recombination with the introduction of GO. Moreover, the simple and affordable solvothermal derived TiO 2 -GO nanocomposite exhibit rapid photocatalytic degradation on MB in 25 min of UV-light irradiation.

Banana peel is a common solid biowaste. This paper reports a sustainable synthesis of carbon quantum dots (CQDs) from banana peel waste by a simple hydrothermal method. The resulting CQDs have a narrow size distribution, and the average particle size was measured as 5 nm. The nitrogen-containing and oxygen-containing functionalities on/in the surface of carbon structure were observed in the resulting CQDs. CQDs emit intense blue fluorescence under the excitation of UV-light (365 nm) with a good quantum yield of 20% without any surface passivation chemicals. Besides, CQDs exhibit excellent water solubility and excitation-dependent emission performance. Furthermore, the banana peel waste-derived CQDs had almost no photobleaching under UV-light irradiation for a long-time, suggesting that they have high photostability. Since no chemical reagent was involved in the synthesis of CQDs, the synthesized CQDs were confirmed to have lower toxicity for nematodes even at a high concentration of 200 μg mL−1. Because of the intense fluorescence with excellent fluorescence stability and biocompatibility, CQDs can be used for bioimaging in nematodes. The CQDs efficiently stained into the whole body of the nematodes and brightly illuminated the multicolor by varying the excitation wavelength. Therefore, fluorescent CQDs would be a great potential candidate for bioimaging applications.

Hollow carbon nanospheres (HCNSs) supported on monodisperse iron oxide nanoparticles (IONPs) were synthesized by a carbonization route using sucrose as the carbon precursor. The resulting product of the obtained HCNSs possessed a narrow size distribution of 15 nm and an interlayer distance of 0.35 nm. The intensity of the D to G value was less than 1, which confirms the obtained HCNSs with graphitization. This study is expected to pave the way for the application of HCNSs in nanoelectronics.

Hydrophilic nitrogen-doped carbon dots (HN-CDs) were produced by a simple hydrothermal method from biowaste, dwarf banana peel. XRD, Raman spectroscopy, and HRTEM analyses confirmed the graphitic structure and narrow size distribution of the HN-CDs. Nitrogen-doping to the carbon structure/framework and owing rich hydrophilic groups on HN-CDs surface were confirmed by XPS and ATR-FTIR spectroscopy techniques. HN-CDs emitted strong and tunable fluorescence (FL) and possessed a good quantum yield (23%). Thus this novel HN-CDs applied as a nanoprobe for the detection of metal ion (Fe3+ ion) in aqueous solution by the fluorometric method. Excessive or lesser amounts of Fe3+ ion in human bodies lead to diverse diseases. Additionally, the accumulation of Fe3+ ion in the environment will escort to a great threat. The prepared HN-CDs selectively and sensitively detect Fe3+ ions by the FL quenching of HN-CDs with a limit of detection of 0.66 μM in the range of 5–25 μM. Further, the HN-CDs employed as a biocompatible probe for the multicolor bioimaging in rat liver cells. Also, HN-CDs used as fluorescent ink for drawing and writing. Thus, the biowaste/biomass successfully turned to a useful nanoprobe for environmental protection and health care.

In this work, green and economical synthesis of highly fluorescent nitrogen-doped carbon nanodots (N-CNDs) is reported using Malus floribunda (M. floribunda) fruit and aqueous ammonia as carbon and nitrogen source, respectively by a simple hydrothermal method. The synthesized N-CNDs show exceptional advantages including acceptable fluorescent quantum yield (18 %) and N-CNDs sizes are around 3.5 nm. The fluorescence of N-CNDs based nanosensor can be selectively and sensitively quenched by ferric ions in the aqueous medium. This phenomenon was used to develop a fluorescent method for facile detection of ferric ions within a linear range of 10–50 μM with a detection limit of 2.5 μM (S/N = 5) having linear regression value (R2) of 0.994. The synthesized N-CNDs incubated with human colon cancer (HCT-116) cells which did not stimulate cell death, indicating that the N-CNDs have good biocompatibility. Hence, the N-CNDs was used as a fluorescent probe for in vitro imaging of HCT-116.TheN-CNDswereuniformly internalized into the whole body of cells and displays the multicolor fluorescence imaging. To best of the authors' knowledge, this is the earliest report on the selective sensing of ferric ions and live-cell imaging using M. floribunda fruit-derived N-CNDs by fluorescent quenching mechanism.

The Malus floribunda fruit extract and aqueous ammonia have been employed as carbon and nitrogen resource material, respectively to synthesize nitrogen-doped carbon dots (N-CDs) by a facile one-step hydrothermal method. The N-CDs exhibit excellent lattice fringes with a d-spacing of 0.21 nm. The N-CDs have tunable fluorescence emission with redshift from 390 to 501 nm as the excitation wavelength increased from 300 to 460 nm. Finally, N-CDs have been used as a fluorescent probe to image Caenorhabditis elegans (nematode) in vivo model. It showed low cytotoxicity and remarkable performance due to its good fluorescence quantum yield (19%). Moreover, the obtained N-CDs are potential candidates for biomedicine-related studies.

In this study, we propose a dye–monomer interaction force measurement technique based on atomic force microscopy (AFM) to predict the performance of polymeric dispersants. Cantilevers modified with functional monomers such as styrene, N-butyl acrylate (BA), and 2-(N-phthalimido)ethyl methacrylate (PEMA) were used to characterize the interaction force between these functional monomers and a target dye (Disperse Blue 359). The interaction forces of each monomer—styrene, BA, and PEMA—with Disperse Blue 359 were measured as 10.75 nN, 7.06 nN, and 21.31 nN, respectively, and their trend was consistent with dipole-moment values obtained from density function theory (DFT) calculations (μ(styrene) = 0.0001, μ(PEMA) = 2.3158, μ(Disperse Blue 359) = 3.0368). We synthesized a series of model polymers containing specific functional monomers (CoPS10, CoBA, CoPPEMAs) with similar molecular weights, molecular-weight distributions, and acid contents and compared their actual performance with that predicted from interaction force measurement data. The results were well correlated with the interaction force measurement data. The effect of the PEMA content on dye dispersion stability was also investigated; the results indicated that both the PEMA content and the type of dye-interacting group greatly influenced the characteristics of the dispersion.

An innovative, facile, low-cost and one-pot hydrothermal carbonization method was developed for the synthesis of bright fluorescence nitrogen-doped carbon dots (NCDs) using Piper betle (Betel) leaf as a carbon and nitrogen precursor. Various advanced physicochemical characterization techniques have been performed to confirm the structural and optical properties of the resulting Betel-derived NCDs (B-NCDs). The as-synthesized B-NCDs exhibited unique excitation-dependent fluorescence behavior, high fluorescence/photochemical stability, exceptional solubility in hydrophilic solvents like water, and good biocompatibility. On the basis of the astounding optical behavior of B-NCDs, they were utilized as a nanoprobe for determination of Fe3+ ion by the fluorometric method. Notably, this nanoprobe was performed by a linear relationship between the fluorescence intensity and the concentration of Fe3+ ion ranging from 5 to 30 μM with a detection limit as 0.43 μM. Highly selective and sensitive determination of Fe3+ ion was carried out through the fluorescence quenching of B-NCDs due to the resonance energy/electron transfer (RET) mechanism. Besides, the resulting B-NCDs employed as a biocompatible probe in multicolor imaging applications of HCT-116 human colon cancer cells. B-NCDs is not only efficient nanosensor for the determination of Fe3+ ion and biocompatible probe for the multicolor imaging. It also would be a substantial alternative for the traditional fluorescent inks due to its extraordinary fluorescence stability, biocompatibility, pollution-free, and easily washable. In this report for the first time, Betel leaf as carbon and nitrogen source was used to synthesize B-NCDs without adding any chemical reagent. Thus it was applied for diverse analysis field.

In this work, an ultra-sensing photoelectrochemical (PEC) glucose biosensor has been constructed from the bio-derived nitrogen-doped carbon sheets (NDC) wrapped titanium dioxide nanoparticles (NDC-TiO2 NPs) followed by the covalent immobilization of glucose oxidase (GODx) on them (designated as a GODx/NDC-TiO2NPs/ITO biosensor). Initially, the TiO2 NPs was synthesized by sol-gel method and then NDC-TiO2 NPs was synthesized utilizing a green source of Prunus persica (peach fruit) through a simple hydrothermal process. The synthesized NDC-TiO2 NPs composite was characterized by FESEM, HRTEM, Raman spectroscopy, XRD, ATR-FTIR spectroscopy and XPS to determine composition and phase purity. These fabricated GODx/NDC-TiO2NPs/ITO biosensor exhibited a good charge separation, highly enhanced and stable photocurrent responses with switching PEC behavior under the light (λ > 400 nm). As a result, GODx/NDC-TiO2NPs/ITO PEC glucose sensor exhibits a good photocurrent response to detection of glucose concentrations (0.05–10 μM) with an ultra-low detection limit of 13 nM under optimized PEC experimental conditions. Also, the PEC glucose sensor revealed a high selectivity, good stability, long time durability, and capability to analyze the glucose levels in real human serum. Also, the further development of this work may provide new insights into preparing other bio-derived carbon nanostructure-based photocatalysts for PEC applications.

Zinc oxide nanoparticles decorated graphene oxide (ZnO@GO) composite was synthesized by simple solvothermal method where zinc oxide (ZnO) nanoparticles and graphene oxide (GO) were synthesized via simple thermal oxidation and Hummers method, respectively. The obtained materials were thoroughly characterized by various physico-chemical techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Raman spectrum shows the intensity of D to G value was close to one which confirms the obtained GO and ZnO@GO composite possesses moderate graphitization. TEM images shows the ZnO nanoparticles mean size of 15±5nm were dispersed over the wrinkled graphene layers. The photocatalytic performance of ZnO@GO composite on degradation of methylene blue (MB) is investigated and the results show that the GO plays an important role in the enhancement of photocatalytic performance. The synthesized ZnO@GO composite achieves a maximum degradation efficiency of 98.5% in a neutral solution under UV-light irradiation for 15min as compared with pure ZnO (degradation efficiency is 49% after 60min of irradiation) due to the increased light absorption, the reduced charge recombination with the introduction of GO. Moreover, the resulting ZnO@GO composite possesses excellent degradation efficiency as compared to ZnO nanoparticles alone on MB.

Despite the superior properties of graphene, the strong pi-pi interactions among pristine graphenes yielding massive aggregation impede industrial applications. For non-covalent functionalization of highly-ordered pyrolytic graphite (HOPG), poly(2,2,2-trifluoroethyl methacrylate)-block-poly(4-vinyl pyridine) (PTFEMA-b-PVP) block copolymers were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization and used as polymeric dispersants in liquid phase exfoliation assisted by ultrasonication. The HOPG graphene concentrations were found to be 0.260-0.385 mg/mL in methanolic graphene dispersions stabilized with 10 wt % (relative to HOPG) PTFEMA-b-PVP block copolymers after one week. Raman and atomic force microscopy (AFM) analyses revealed that HOPG could not be completely exfoliated during the sonication. However, on-line turbidity results confirmed that the dispersion stability of HOPG in the presence of the block copolymer lasted for one week and that longer PTFEMA and PVP blocks led to better graphene dispersibility. Force-distance (F-d) analyses of AFM showed that PVP block is a good graphene-philic block while PTFEMA is methanol-philic.

The ability to disperse pristine (unfunctionalized) graphene is important for various applications, coating, nanocomposites, and energy related systems. Herein we report that amphiphilic copolymers of poly(4-vinyl pyridine)-block-poly(ethylene oxide) (PVP-b-PEO) are able to disperse graphene with high concentrations about 2.6mg/mL via sonication and centrifugation. Ethanolic and aqueous highly-ordered pyrolytic graphite (HOPG) dispersions with block copolymers were prepared and they were compared with the dispersions stabilized by P-123 Pluronic® (P123) and poly(styrene)-block-poly(ethylene oxide) (PS-b-PEO) synthesized. Transmission electron microscopy, scanning electron microscopy, atomic force microscopy, X-ray diffraction, Raman and UV-visible spectroscopic studies confirmed that PVP-b-PEO block copolymers are better stabilizers for HOPG graphene than P123 and PS-b-PEO. X-ray photoelectron spectroscopy and force-distance (F-d) curve analyses revealed that the nitrogen of vinyl pyridine plays a vital role in better attractive interaction with surface of graphene sheet. Thermogravimetric analysis showed that larger amount of PVP-b-PEO was adsorbed onto graphene with longer poly(4-vinyl pyridine) (PVP) block length and in aqueous medium, respectively, and which was consistent with electrical conductivity decreases. This study presents the dispersion efficiency of graphene using PVP-b-PEO varies substantially depending on the lengths of their hydrophobic (PVP) domains.